1. Field of the Invention
The invention relates to a vision aid for the amblyopic population, inclusive of patients with age-related macular degeneration (AMD) or other low vision conditions. The vision aid is an intra-ocular lens (IOL) device that has multiple focusing powers or optics.
2. Discussion of Related Art
Age-related macular degeneration (AMD) patients usually have impaired central visual fields and often rely heavily on peripheral vision for daily tasks. Peripheral retina has low receptors (cons and rods) densities, which lead to their poor resolution ability. Low vision patients, such as the amblyopic population, also have poor retina resolutions. For these patients, the bottle neck of visual resolution is at retina resolution. Improving optical imagery in details does not solve the problem of poor visual resolution.
AMD patients often have compromised fovea. However, there are still functional retina receptors surrounding the compromised receptors. These functional retina receptors are often peripherally located and have larger spacing between each other. The increase spacing leads to decreased image resolution ability of the retina. For example, at 3 degrees nasal retina, the visual acuity is reduced to 0.4 compared to the 1.0 visual acuity at 0 degrees; at 5 degrees nasal retina, the visual acuity is reduced to 0.34 compared to the 1.0 visual acuity at 0 degrees (Millodot, 1966).
There are three basic types of vision aids available conventionally either individually or in combination.
The first type is a single telescope as the visual aid. The telescopes are often mounted on the spectacles, which are heavy and are not appealing cosmetically. Implanted telescopes often require very large incisions during surgery to implant. The main disadvantage of using a telescope system alone is the resultant narrow visual field of view and overall poor image quality, which could cause a safety concern during motion.
The second type of vision aid is a prism. The prism is to realign the line of sight to the peripheral retina. This application needs to overcome a binocular fusion problem in order to avoid double imagery. Also, the prism does not magnify the retinal images. Therefore, the problem of low visual resolution due to the larger peripheral retina receptor spacing is not resolved.
The third type of vision aid is a magnifying glass, sometimes combined with a prism. This visual aid is often used as a desk mount device, which limits the application range for patients. The handheld version of this visual aid has vision instability and focus problems for patients with hand tremors.
Therefore, there are needs to 1) keep a larger visual field of view, 2) increase portability for application, 3) improve cosmetics, and 4) increase the quality of vision and the stability of the application.
FIG. 1 shows Peripheral Visual Acuity from Bennett and Rabbetts “Clinical Visual Optics” page 37, Butterworth, Boston, 1984.
It is known that the peripheral vision can still provide adequate resolution. The resolution, however, is progressively reduced (FIG. 1). As shown in FIG. 1, visual acuity is reduced to 0.5 at 2 degrees nasally, to 0.4 at 3 degrees nasally, to 0.34 at 5 degree nasally, relative to the 1.0 visual acuity at 0 degrees. Temporal, superior and inferior peripheral retinas are expected to have similar behavior at similar small degree off axis range. Accordingly, increasing or magnifying retina image size relative to the size associated with 14 inches reading distance could allow the peripheral retina to enable visual acuity comparable to that of central 0 degrees retina. In particular, the magnification could be 2 times for using 2 degrees peripheral retina, 2.5 times for using 3 degrees peripheral retina, or 3 times for using 5 degrees peripheral retina.
Bifocal and multifocal optics are well known in the ophthalmic optics field. Alcon's ReSTOR® lens optics is an example. However, existing ophthalmic bifocal or multifocal optics have much lower add power by design because they are obligated to suit different patient needs. The ReSTOR® lens has a 4 D IOL add power which is likely the highest add power known for commercially available products. Table 1 indicates that with a 4 D add power the magnification is only 1.2 times. That 1.2 times value is not likely to be adequate for AMD application according to the needs shown in FIG. 1. That is, 1.2 times magnification is only useful if the 0.5 degrees retina is not damaged by AMD.